SIR – Lexington (January 12th) dismissed the idea that armed civilians can be a “bulwark against tyranny” as “an appeal to narcissism”. But consider America’s history. Robert Williams, a civil-rights leader in North Carolina, called for “armed self-reliance” for blacks in order to thwart violence from racist whites. The Ku Klux Klan sought gun controls for the opposite reason.

In the 1920s thousands of armed coalminers in West Virginia assembled to claim their rights from union-busting authorities who wielded bomber planes and gas. Frank Keeney, a pioneering union official, observed that “the only way you can get your rights…is with a high-powered rifle.” In today’s America Pink Pistols is an organisation that promotes gun ownership as a means of self defence for gays who are attacked.

Marginalised Americans have sometimes seen guns as an option when protection from the state has fallen a few “bulwarks” short.

John BninskiWilliamsburg, Virginia

London’s meat market

SIR – The journalist in 1855 who described London’s Smithfield market as a “continued protest against good sense” was not referring to the site we have today but to the ancient livestock market on that spot that was closed in 1855 and moved to Islington (”Meat hook”, January 12th). It was an entirely appropriate remark. The livestock market had been a nuisance and subject of complaint since the 18th century, and was still partly supplied by driving herds of cattle through Oxford Street.

The old Smithfield site lay derelict until the present meat market was opened in 1868. At that time the site had a lot more to recommend it than it has today. Originally the Metropolitan Railway passed underneath, allowing the market to receive much of its meat by large hydraulic lifts directly from the network of platforms and sidings beneath it. But the railways stopped carrying meat after 1950, so Smithfield now makes as much “good sense” as a meat market as its predecessor did as a livestock market. However, there is a case for preserving some of the remaining buildings for other uses.

Richard PerrenAberdeen

A point worth repeating

SIR – Regarding the financial crisis in Ireland, Charlemagne wrote that “There is much blame to spread for what went wrong in the past; for every irresponsible borrower there was an irresponsible lender” (January 12th). This implies a symmetry that is simplistic at best, dishonest at worst.

Bank presidents have a fiduciary duty to their shareholders to engage in responsible lending practices, maintain adequate capital and loan loss reserves and avoid unduly risky behaviour that could jeopardise the survival of their institutions. It is safe to say that all of these elements were lacking in the run-up to the Irish financial crisis.

If bank presidents, and the government agencies responsible for overseeing them, had done their jobs this crisis never would have happened.

SIR – I was entertained by your article on French doublespeak under the new Socialist government (“Lost in translation”, January 12th). However, your glossary omitted what I consider to be the classic establishment euphemism: a plan de sauvegarde d’emploi (plan for preserving jobs), usually abbreviated to PSE.

I recently joined a company in Paris just after a PSE and the large number of empty desks was testament to its true meaning.

Giles PicklesParis

Intervening in Mali

*SIR – Fools rush in where wise men fear to tread (“Get stuck in but don’t get stuck”, January 19th). Mali is a very dangerous and unpredictable place. The Malian government is in effect a military dictatorship and only represents a fraction of the population.

The Tuareg tribes who live in the north-east have a large number of unresolved long term grievances against the central government. They are tough desert fighters and armed to the teeth as a result of their participation in the revolution in neighbouring Libya. Who the opposition are is unclear. Some appear to be militant Muslim extremists but many more are seekers of a fairer political arrangement in which their interests would be given proper consideration.

For all of these reasons Canada would be well advised to stay as far as possible away from Mali. I am nervous about our current very limited involvement and hope it will end soon. I expect the fighting to be long and bitter and to involve guerrilla fighting and acts of international terrorist revenge. If François Hollande wants to involve France in a military adventure that is his business but he should stop trying to drag us in.

Garth EvansVancouver* SIR – Your leader on Mali suggested that the jihadists in Algeria acted in “sympathy with their Malian brethren” by attacking the gas facility. I would have thought that such attacks are prepared and timed months before they actually happen. Unless you think the jihadists foresaw the French military intervention in Mali months before it happened, my guess would be that the timing of those two events was a coincidence.

Ramzi RafihLondon

Let the inventors speak

SIR – It was heartening to read your attempt at counteracting the recent techno-pessimism (“Has the ideas machine broken down?”, January 12th). It was less encouraging to see the debate conducted in wholly economic terms of growth and productivity. The reality is that substantive economic theories of technological and scientific change are surprisingly recent. And most of those theories often naively conceptualise the complex process of knowledge generation in terms of “ideas machines”, reducing the often unknown rewards of scientific progress to unsatisfying claims about relative increases in productivity.

The failure of economic theory accurately to describe technological change is too often mistaken as a failure of innovation itself. As incisive as Tyler Cowen’s thoughts on the feasibility of technological gains may be, surely we would benefit from hearing more from practitioners who actually understand the current state of scientific and technological research. Save for a brief reference to Ray Kurzweil, you gave no voice to the remarkable innovators over whose bent heads blowhards proclaim the death of innovation.

Samuel BjorkOxford

SIR – As the digital age loses steam it is easy to let ourselves think that we have run out of good ideas (“The great innovation debate”, January 12th). But in the 17th century, the printing press catalysed the sharing of information, sowing the seeds for the Industrial Revolution. The explosion of information in the 21st century can do the same. Gains in digital communication can unlock tangible technology.

Hardware and software work in sync in robotics, energy generation and nanotechnology. There are still plenty of gains to be made from the innovation that is needed in energy, materials, transportation and infrastructure. Let’s not limit our horizons by writing off two-and-a-half centuries of growth. I doubt that Michael Faraday realised at the time that his discoveries would unlock two centuries of invention.

Sir James DysonMalmesbury, Wiltshire

* SIR – The slowing of the growth rate in labour productivity could be the result of the financial crisis, and not because of a diminishing flow of innovations. Banks have radically cut their lending, inhibiting growth to an economy’s stock of capital. And with higher unemployment, wages have fallen. When capital gets scarce and labour becomes relatively cheap and available, employers naturally substitute labour for capital wherever their production processes permit.

The reduced rate of growth of capital per employee reduces that of output per employee. That happens, not because of a lack of innovations, but simply because the economic environment has encouraged a rethink about how much capital to use relative to labour in the productive process.

Substitution of labour for capital is a rare event, which will probably pass into history as the shock of the financial crisis fades. Until then it will be premature to conclude that innovation is running out of steam.

J.R. SargentHonorary professor of economicsUniversity of Warwick

SIR – Another useful insight is provided by something akin to Amdahl’s law in computer design, which holds that even if some components of a system are improving, the parts that are not improving will eventually dominate the performance of that system.

For example, for flights that are under 2,000 miles a person will spend more time travelling to and from the airport, checking in at the airport, going through security and waiting for his bags than time spent up in the air. Increases in aircraft speed would have less benefit than shortening the other bits of the journey time.

Tim JoslingLeura, Australia

SIR – One factor underlying the lack of innovation ironically may be peace. Unlike purely economic crises, which often do not lead to technological advances, physical wars bring big R&D investments.

Marc FolchToronto

SIR – The explanation as to why productivity has slumped since 2004 is a simple one. That year coincided with the creation of Facebook.

Nikko SchaffRochester, New York

SIR – Your apt choice of the humble toilet to illustrate the best innovations brought to mind this shrewd comment from the author Brian Aldiss: “Civilisation is the distance man has placed between himself and his excreta”.

Frank MottÉpaney, France

* SIR – You say that we live in “straightened times” (“The great innovation debate”, January 12th).